Production of benzyl alcohol and benzaldehyde



United States Patent 15 Claims. (Cl. 260599) ABSTRACT OF THE DISCLGSUREBenzyl alcohol and benzaldehyde are produced by oxidizing liquid tolueneat 170 C.220 C. with gas containing less than 21% of oxygen until notmore than of the toluene has been oxidized, then preferably decomposingthe hydroperoxides formed, and isolating the benzyl alcohol andbenzaldehyde produced.

The present invention relates to the oxidation of toluene to benzylalcohol and benzaldehyde.

The most widely used industrial process for the preparation of benzylalcohol and benzaldehyde consists in chlorinating toluene to a mixtureof benzyl chloride and benzylidene chloride, which are then saponified.The

benzyl alcohol and the benzaldehyde thus obtained con tain chlorinatedimpurities, the elimination of which by distillation, or chemically, isalways difficult, but is also essential when these products are intendedfor use in perfumery, as pharmaceutical products, or as intermediates inorganic syntheses. Moreover, these chlorinated impurities are liable tocause corrosion, which necessitates the use of special materials.

It is possible to prepare benzaldehyde by catalytically oxidizingtoluene in the vapour phase at temperatures from 300 to 500 C. Theyields do not exceed 30-50% (see Ullmanns Enzyklopaedie, vol. 4, 238(1953)). The process is dangerous to perform industrially because themixture of toluene vapour and air used is explosive.

In addition, the oxidation of toluene in the liquid phase has beendescribed. It is known that when hydrocarbons are oxidized, the firststage of the oxidation is the formation of hydroperoxides and that firstalcohols and then aldehydes (or ketones) are formed from thehydroperoxides, both of which may subsequently be oxidized to thecorresponding acids. In the liquid phase oxidation of toluene, all theoxidation stages have been observed. The problem is therefore to controlthe oxidation in such a manner as to obtain the maximum yield of benzylalcohol and benzaldehyde, or of their precursor benzyl hydroperoxide,which can be readily converted into benzyl alcohol and benzaldehyde in asubsequent operation.

The previously described processes for oxidizing toluene in the liquidphase have given only negligible yields of benzyl alcohol andbenzaldehyde. While. the preparation of benzyl hydroperoxide fromtoluene has been described, it has only been possible to obtain thishydroperoxide in the presence of a considerable quantity of a peroxidicinitiator, viz, cumene hydroperoxide (see United States patentspecification No. 2,683,751). The separation of benzyl hydroperoxide, orof benzyl alcohol and benzaldehyde, from the product of this reaction isvery ditficult because of the presence of the cumene hydroperoxide orits reduction and degradation products. If the oxidation of toluene iscarried out in the presence of catalysts such as heavy metals,substantially only benzoic acid is ob tained.

It has now been found that toluene may be oxidized in the liquid phaseunder certain specific conditions in 3,387,036 Patented June 4, 1968good yields to a mixture of benzyl alcohol and benzaldehyde. The processof the invention comprises oxidizing liquid toluene at 220 C. withgaseous oxygen in the presence of an inert gaseous diluent in amountsuch that the gaseous mixture contains not more than 21% of oxygen, theoxidation being discontinued when at most 10% of the toluene has beenoxidized. In this process the diluted oxygen, preferably air of reducedoxygen content, is passed through the liquid toluene at a temperaturebetween 170 and 220 C. under a pressure sufficient to maintain thetoluene in the liquid state, in the absence of any metallic catalyst orperoxidic initiators, other than those formed from the toluene, and theoxidation is stopped at a degree of conversion of the toluene at mostequal to 10%. A mixture of toluene, benzyl hydroperoxide, benzylalcohol, benzaldehyde, benzoic acid and a few other by-products is thusobtained. This mixture is then ordinarily de-peroxidized, for example bycatalytic hydrogenation or by heating in an inert atmosphere to 180-280C., or to a lower temperature if the de-peroxidation is accelerated bythe use of a de-peroxidation catalyst, such as a cobalt salt or aderivative of boric acid (eg the anhydride, an acid, or an ester). Whenthe peroxide has been decomposed, the acid products are eliminated bywashing with an aqueous alkali metal hydroxide solution, and theresidual organic layer is then fractionally distilled.

When the crude oxidation product contains only a small proportion ofhydroperoxide, the de-peroxidation treatment may optionally be omitted,since adequate deperoxidation generally takes place in the separation ofthe constituents of the mixture.

It is preferred to oxidize the liquid toluene in the presence of astabilizing agent for organic hydroperoxides so that the decompositionof the benzyl hydroperoxide, which is a primary product of theoxidation, is inhibited. The mixture obtained is then subsequentlyde-peroxidized and separated as already described. As stabilizing agent,the products known for stabilizing hydrogen peroxide may be used, e.g.those appearing in the list given in R. E. Kirk and D. F. Othmer(Encyclopedia of Chemical Technology, Interscience Encyclopedia, NewYork, vol. 7, p. 730 (1951)). More especially, sodium pyrophosphate andsodium fluoride may be used. The proportion of stabilizing agent to beemployed is conveniently between 0.01% and 0.5% by weight of the tolueneemployed.

The process of the invention gives a mixture of benzyl alcohol andbenzaldehyde in yields from 50% when no stabilizer is employed, to 70%when a stabilizer is used.

The following examples illustrate the invention and show how it can beput into practice:

EXAMPLE 1 Into a stainless steel autoclave having a capacity of 3.6litres and provided with a stirring system are introduced 2000 g. oftoluene, and a pressure of 10 bars is established with a gas mixtureconsisting of 10% of oxygen and 90% of nitrogen. After heating to 165C., when the pressure reaches 12 bars, a current of the same gas mixtureis introduced into the reaction mass at a rate of 350 litres per hour,the heating being continued until the temperature reaches -190 C. At theend of one hour, the heating and the passage of the gas mixture arestopped.

The percentage by weight of the oxidation products is determined on analiquot fraction of the reaction product by evaporation of the toluenein vacuo, followed by determination of the benzyl hydroper-oxide byiodometry and of the acid products (expressed as benzoic acid) by alkalititration. From the difference, the percentage of the oxidation productsother than hydroperoxides and acids is obtained. The results are set outin Table I below.

The crude mixture is washed with 200 cc. of aqueous sodium hydroxidesolution, the aqueous layer is separated, the toluene is driven oif fromthe organic fraction, and the residue is distilled. Benzyl alcohol,benzaldehyde and by-products are obtained in the yields shown in TableII below.

EXAMPLE 2 The procedure of Example 1 is followed, but 0.1% by Weight ofsodium pyrophosphate is added to the toluene. Analyses, carried out asin Example 1, give the results shown in Table I.

0.001% of cobalt in the form of cobalt Z-ethylhexanoate is added to thecrude oxidation mixture, the autoclave is purged with nitrogen and theproduct is rapidly heated to 165 C., While the inert atmosphere ismaintained by bubbling nitrogen through the mixture. At the end ofminutes it is found by titration of an aliquot portion that no peroxideremains in the reaction mass. The latter is washed with 200 cc. of a 5%aqueous sodium hydroxide solution, the acqueous layer is decanted, andthe organic layer is concentrated by distillation of the toluene invacuo. The benzyl alcohol and the benzaldehyde are then separated fromthe other oxidation products, by fractional distillation under a vacuumof 7 mm. Hg, the aldehyde passing over at 4950 C. and the alcohol at8283 C. The yields obtained are set out in Table II.

EXAMPLE 3 The procedure of Example 1 is followed, but 0.1% by weight ofsodium fluoride is added to the toluene. The composition of the mixtureafter oxidation, determined as indicated in Example 1, is given in TableI.

TABLE I lizer (Example 2) Benzyl alcohol percent 30. 2] 38 l Benzaldehydcjpercent 19. 2f 4 32. 3 J 3 Benzoic acid 16 14. 5Non-recoverable lay-products. 34

Although the foregoing examples describe a batch-wise process, theprocess may also be carried out continuously.

We claim:

1. Process for the production of benzyl alcohol and benzaldehyde whichcomprises oxidizing liquid toluene at 170 C.220 C. with a mixture ofgaseous oxygen and an inert gaseous diluent such that the said mixturecontains not more than 21% of oxygen, until at most 10% of the toluenehas been oxidized, decomposing the hydroperoxides formed to benzylalcohol and benzaldehyde by catalytic hydrogenation and separating thebenzyl alcohol and benzaldehyde produced.

2. Process according to claim 8 in which, after the oxidation, thehydroperoxides in the oxidized toluene are decomposed by heating in aninert atmosphere in the presence of a cobalt salt.

3. Process according to claim 1 in which the gaseous mixture is air ofreduced oxygen content.

4. Process according to claim 1 in which the oxidation is discontinuedwhen 4% to 7% of the toluene has been oxidized.

5. Process according to claim 1 in which the oxidation is carried out inthe presence of a stabilizing agent for organic hydroperoxides.

6. Process according to claim 5 in which the stabilizing agent is sodiumpyrophosphate used in amount of 0.01 to 0.5% by weight of the toluene.

7. Process according to claim 5 in which the stabilizing agent is sodiumfluoride used in amount of 0.01 to 0.5% by Weight of the toluene.

8. Process for the production of benzyl alcohol and benzaldehyde whichcomprises oxidizing liquid toluene at C.220 C. with a mixture of gaseousoxygen and an inert gaseous diluent such that the said mixture containsnot more than 21% of oxygen, until at most 10% of the toluene has beenoxidized, decomposing the hydroperoxides formed to benzyl alcohol andbenzaldehyde by heating in an inert atmosphere, and separating thebenzyl alcohol and benzaldehyde produced.

9. Process according to claim 8 in which the gaseous mixture is air ofreduced oxygen content.

10. Process according to claim 8 in which the oxidation is discontinuedwhen 4% to 7% of the toluene has been oxidized.

11. Process according to claim 8 in which the oxidation is carried outin the presence of a stabilizing agent for organic hydroperoxides.

12. Process according to claim 11 in which the stabilizing agent issodium pyrophosphate used in amount of 0.01 to 0.5 by weight of thetoluene.

13. Process according to claim 11 in which the stabilizing agent issodium fluoride used in amount of 0.01 to 0.5% by Weight of the toluene.

14. Process for the production of benzyl alcohol and benzaldehyde whichcomprises oxidizing liquid toluene at 170-220 C. with air of reducedoxygen content in the presence of 0.01 to 0.5% by weight of the tolueneof sodium pyrophosphate until 4 to 7% by weight of the toluene has beenoxidized, decomposing the benzoyl hydroperoxide formed by heating in aninert atmosphere in the presence of a cobalt salt, and isolating benzylalcohol and benzaldehyde from the product by fractional distillation.

15. Process for the production of benzyl alcohol and benzaldehyde whichcomprises oxidizing liquid toluene at 170-220 C. with air of reducedoxygen content in the presence of 0.01 to 0.5% by weight of the tolueneof sodium fluoride until 4 to 7% by weight of the toluene has beenoxidized, decomposing the benzoyl hydroperoxide formed by heating in aninert atmosphere in the presence of a cobalt salt, and isolating benzylalcohol and benzaldehyde from the product by fractional distillation.

References Cited UNITED STATES PATENTS 1,902,550 3/1933 Forrest et a1260599 X 2,199,585 5/1940 Bone 260599 2,347,434 4/1944 Reichert et al.260-610X BERNARD HELFIN, Primary Examiner.

